The amount of counterfeit money surfacing over the first half of 2011 fell sharply by 24 percent from a year ago, the State Bank of Vietnam said Thursday.

According to the central bank, 44 percent of the counterfeit banknotes were VND50,000 bills while 28 percent were VND100,000 notes.

Circulation of counterfeit money declined because polymer bills are easy to check by the public thanks to different features, including faint images and the security strip, the central bank said. The amount of fake money fell by 60 percent from the first half of 2009, it added.

Vietnam started to switch to polymer notes in 2002, gradually replacing paper-based money. Coins are also available in small denominations between VND200 and VND5,000.

The Ministry of Public Security said last month it was looking into allegations that a Vietnamese official accepted bribes in exchange for providing a contract with Australian currency-maker Securency to print the polymer bills in Vietnam.